1. Field
The present invention relates generally to content protection and security in computer and consumer electronics systems and, more specifically, to watermark detection.
2. Description
A number of systems for protecting content (e.g., against unauthorized copying) have been developed that employ watermarking as a part of the protection scheme. Watermarking is a technique whereby information is embedded into content in such a way that is generally transparent to users of the content, is difficult to remove from the content, and can be robustly detected in the content by specialized hardware or software. In some systems, the watermark data may indicate conditions and requirements constraining use of the content, including constraints specific to copying, with the intent that such information is robustly carried with the content when in an analog or unencrypted digital form. A recording device that is compliant with such a system may be required to detect the watermark in unencrypted content that is to be copied. If the watermark is present and indicates that a copy is not permitted, then the recording device does not make a copy. If the watermark is present and indicates that a copy is permitted, the recording device may be required to apply cryptographic protection (i.e., encryption) to any authorized copy of that content made by the recording device. In that case, compliant player devices may be required to detect the watermark in unencrypted recordings that are to be played, and stop playback if the watermark is detected (since such content either should not have been recorded, or should have been recorded in a cryptographically protected manner).
Unfortunately, real world properties of watermark technologies lead to challenging practical problems when watermarks are used in such a manner.